1. Field of the Invention
The present invention relates to controlled release products such as controlled release fertilizer products. More particularly, it relates to coated products in particulate form which are structured to provide release profiles wherein initial release of active ingredients such as fertilizer nutrients therefrom is suppressed or inhibited for a predetermined period and longevity for release the active ingredients is within a period of time of 60 days or less after the time of application. The invention further relates to the use of such products, particularly, as potting soil starter fertilizers and to processes for producing particulate products exhibiting the desired release profiles.
2. Description of Related Art
The use of controlled release products such as controlled release fertilizer compositions to provide nutrients in growing media has been well known for a long period of time heretofore. Also, it has been known heretofore that the presence of additional nutrients in growing media may be beneficial depending on when these additional nutrients are made available to the plants growing in these media. However, the availability of too many nutrients can be detrimental to the plants. Furthermore, the presence of too much available nutrients can be considered not only an inefficient use of fertilizer, but also a threat to the environment.
Thus, it has been recognized previously that delivery of the correct amount of nutrients at the correct time is crucial for growing plants. However, with conventional water-soluble fertilizers optimal delivery of nutrients can only be achieved by employing very labor intensive methods. Alternatively, correct delivery of nutrients for nutrient uptake by plants can be achieved by modification of the fertilizer products such as by chemical means to reduce the solubility of the nutrients, or by physical means such as by coating or encapsulating the fertilizer compositions.
Likewise, it has been recognized heretofore that the controlled release of other water soluble core materials such as insecticides, herbicides, fungicides, pheromones, biostimulants, growth regulators and the like within a predetermined time period would be advantageous from a utilitarian and commercial standpoint.
With specific regard to coated or encapsulated fertilizers, such products are known to be very effective sources for providing controlled release of nutrients for growing of plants. In such products, the nutrients are released at controlled rates, resulting in sustained feeding of plants treated with the fertilizer. As a result, a single application of these so-called controlled release fertilizers (CRFs) can provide the necessary nutrients that would take multiple applications of soluble fertilizers.
The types of coatings that may be applied to soluble core materials such as fertilizer particles to produce CRFs include impermeable coatings, impermeable coatings with tiny pores, and semi-permeable coatings. Typical examples of CRFs with an impermeable coating are sulfur-coated fertilizers such as those disclosed in U.S. Pat. No. 4,636,242. With such sulfur-coated fertilizers, the release of nutrients from the sulfur-coating occurs by diffusion through imperfections in the sulfur coating and through coating breakdown followed by a relatively rapid release of nutrients.
Polymer/sulfur-coated fertilizers such as those disclosed in U.S. Pat. No. 5,405,426 and U.S. Pat. No. 5,219,465 are hybrid products that utilize a primary or inner coating of sulfur with a secondary or outer polymer coating. The nutrient release mechanism in such products results from a combination of water diffusion through the polymer coating and subsequently water penetration through the defects in the sulfur coating. Thus, the release properties of such polymer/sulfur-coated fertilizers are more uniform, and approach those of polymer-coated fertilizers, but at a reduced cost.
Polymer-coated fertilizers are considered to present a more technically advanced approach for controlling the release characteristics. Polymer coatings for soluble nutrient sources may be either impermeable coatings with tiny pores or semi-permeable coatings. The addition of a special surfactant to an impermeable coating material results in microscopic pores. Water diffuses through these pores into the core fertilizer granule dissolving the nutrients. The amount of surfactant in the coating determines its porosity and as a result its release characteristics (typical examples of these CRF products are sold with the trademark Nutricote(copyright)). It should be noted that, although these products cover a wide time period of release (from 40 days up to 12 months), these type of CRFs have the disadvantage that they always require the addition of a special compound in order to achieve the desired release profiles.
Semi-permeable polymeric coatings used for coating CRFs can be categorized as based either on thermoplastic (such as disclosed in U.S. Pat. Nos. 4,019,890 and 5,186,732) or on thermosetting (such as disclosed in U.S. Pat. Nos. 3,223,518 and 4,657,576, and sold with the trademark Osmocote(copyright)) resins. The presence of a polymeric coating on CRFs allows for a rather uniform and consistent nutrient release, provided that the barrier properties of the coating are sufficient. In such products, the release essentially is determined by the coating thickness alone. With some polymer-coated fertilizers, a relatively high initial rate of nutrient release is observed within the first 24 hours after application which is followed by a decreasing nutrient release rate for an extended period thereafter.
The application of a second polymeric coating may compensate for the high initial release rate, thus resulting in CRF products exhibiting delayed release (such as disclosed in U.S. Pat. No. 5,652,196). The most technically advanced state of the art in CRFs with delayed release characteristics comprises single layer coated products (such as disclosed in U.S. Pat. No. 5,993,505). The latter compositions are structured to provide a cumulative release of nutrients of less than 10% of the total nutrients within 30 days after exposure to moisture.
A general characteristic of the presently available commercial CRF products with semi-permeable coatings, such as the Osmocote(copyright) type products, is that these products provide a controlled release of nutrients for relatively long periods of time. Although the release rate of the nutrients out of the CRF products depends on several factors, the only one presently being used in practice to control the length of the release is the amount of coating. The generally accepted method of producing CRF products with different release periods is by using a coating material with high barrier properties at varying coating amounts or thicknesses.
The CEN (Comitxc3xa9 Europxc3xa9en de Normalisation) TC 260/WG 4/Task Force (hereinafter referred to as xe2x80x9cthe CEN TC 260) has provided a standard definition for controlled or slow-release fertilizers. Under that definition, a product may be considered a CRF if the release profile of the product meets the following criteria:
(1) No more than 15 weight percent (wt. %) of core material is released from the fertilizer product within the first 24 hours after application of the product, at ambient temperature;
(2) No more than 75 weight percent (wt. %) of core material is released from the fertilizer product within 28 days after application of the product, at ambient temperature; and
(3) At least 75 weight percent (wt. %) of core material is released from the fertilizer product within a predetermined release time after application, at ambient temperature.
With regard to criterion 1 above, it should be noted that this standard is applied to all of the controlled release products of the present invention in defining the suppressed or inhibited initial release characteristics thereof. Concerning criterion 3 above, it should be further noted that for purposes of the present invention, the predetermined release time after application, at ambient temperature, of the controlled release products is 60 days or less. Therefore, the term xe2x80x9clongevityxe2x80x9d as employed herein defines the time period of 60 day or less between the time of application of core material from the product and the time at which about 75 weight percent (wt %) of the active ingredients such as fertilizers, insecticides, herbicides, fungicides, pheromones, biostimulants, growth regulators and the like and mixtures thereof is released.
A recognized shortcoming of presently available CRF products with semi-permeable coatings is that, as a result of the focus on using coatings with high barrier properties, the range of CRF release periods provided by these products covers release periods from 60 days up to 18 months at ambient temperatures, depending only on the amount of coating applied. In such cases, as soon as sufficient coating material is applied to adequately cover the fertilizer granules (which in general is the case after applying lower coating weights, such as 5 wt. % of coating), the resulting product will exhibit a longevity of more than 60 days from the time of application of the product to a plant, at ambient temperatures, as a result of the barrier properties of the coatings employed. However, if the amount of such coating applied is decreased in an attempt to reduce the longevity of the products below 60 days, it has been found that insufficient coating material is provided to adequately cover the granules and a significant amount of imperfectly coated granules are created. Consequently, these granules release too many nutrients in the first few days, rendering such coated product unsuitable for controlled release products.
Thus, there has been a need heretofore for fertilizer products which have semi-permeable coatings and which have a longevity of 60 days or less and meet the criteria for the fertilizer to be considered a CRF as defined by the CEN TC 260 standard, particularly, in terms of criteria 1 and 2 set forth above. For example, under criterion 1, initial release of not more than 15 wt. % of core material from the product would have to occur within 24 hours after application and under criterion 2 for a a product to be classified as a CRF, as defined by CEN TC 260, the shortest longevity of the fertilizer product would have to be 28 days since not more than 75 wt. % of core material could releases from the product within 28 days after application. No fertilizer products have been known, heretofore, that comply with criteria 1 and 2 set forth under the CEN TC 260 standard when combined with criterion 3 when the predetermined period thereunder is 60 days or less.
Furthermore, in addition to fertilizer products, it should be recognized that no controlled release products have been known heretofore which exhibit release profiles wherein water soluble core materials such as insecticides, herbicides, fungicides, pheromones, biostimulants, growth regulators and the like are released at a rate such that initial release of core material from the product is suppressed so that less than about 15 wt % of core material is released from the product within a 24 hour period after application of the product and wherein longevity of release, at ambient temperature, between the time of application and the time at which at least about 75 wt % of the core material is released from the product is 60 days or less
It is a principal object of the present invention to provide controlled release products which display specific release profiles and, particularly, to coated products such as fertilizer products which exhibit release of active ingredients (such as nutrients) within a relatively short period of time (longevity less than 60 days) in combination with a suppressed initial release period. A further principal object of this invention is to provide processes for producing such controlled release products. Another important object of the invention is to provide controlled release products such as fertilizer products which exhibit a longevity ranging between about 1 day and 60 days, preferably between about 28 and about 49 days but, also, less than 28 days.
A further significant object of the invention is to provide a controlled release fertilizer product having particulate nutrient core material encapsulated in a semi-permeable coating layer wherein the product exhibits a release profile wherein initial release of core material from the product is suppressed so that less than about 15 weight percent of core material is released from the product within a 24 hour period after application of the product and wherein longevity of release, at ambient temperature, between the time of application and the time at which at least about 75 weight percent of the core material is released from the product is 60 days or less.
A still further object is to provide controlled release products having the above described characteristics which are adapted for use as potting soil starter fertilizers.
Accordingly, a controlled release product in accordance with the present invention exhibits a suppressed initial release period and a predetermined longevity of 60 days or less. Such a product comprises:
(a) a particulate core material comprising at least one water soluble composition selected from the group consisting of fertilizers, insecticides, herbicides, fingicides, pheromones, biostimulants, growth regulators and mixtures thereof; and
(b) a semi-permeable coating layer applied on the core material for controlling the release rate of the core material;
(c) the semi-permeable coating layer being formulated in accordance with the following equation to provide a release rate wherein initial release of core material from the product is suppressed so that less than about 15 weight percent of core material is released from the product within a 24 hour period after application of the product and wherein longevity of release, at ambient temperature, between the time of application and the time at which at least about 75 weight percent of the core material is released from the product is 60 days or less:   WVTR  =            φ      ·      δ              π      ⁢              xe2x80x83            ⁢              d        2            
wherein:
(i) WVTR is the water vapor transmission rate of the semi-permeable coating expressed in gramsxc2x7xcexcm/meters2xc2x7day;
(ii) xcfx86 is the water diffusion rate (water flux) through the semi-permeable coating expressed in grams/day;
(iii) xcex4 is the thickness of the coating layer expressed in xcexcm; and
(iv) d is the average diameter of the particulate core material expressed in meters
In a preferred embodiment of the invention, it has been found that one or more of the above-identified objects and others, can be accomplished by utilizing specific coating material having a water vapor transmission rate (WVTR) preferably, greater than about 800 gxc2x7xcexcm/m2xc2x7day; and most preferably, greater than about 900 gxc2x7xcexcm/m2xc2x7day (for example, employing a coating based on a modified cyclo oil alkyd resin); and applying the coating material at a coating thickness of about 20 to about 110 xcexcm.